title: Fitness consequences of outcrossing in a social spider with an inbreeding mating system.
abstract: Inbreeding mating systems are uncommon because of inbreeding depression. Mating among close relatives can evolve, however, when outcrossing is constrained. Social spiders show obligatory mating among siblings. In combination with a female-biased sex ratio, sib-mating results in small effective populations. In such a system, high genetic homozygosity is expected, and drift may cause population divergence. We tested the effect of outcrossing in the social spider Stegodyphus dumicola. Females were mated to sib-males, to a non-nestmate within the population, or to a male from a distant population, and fitness traits of F1s were compared. We found reduced hatching success of broods from between-population crosses, suggesting the presence of population divergence at a large geographical scale that may result in population incompatibility. However, a lack of a difference in offspring performance between inbred and outbred crosses indicates little genetic variation between populations, and could suggest recent colonization by a common ancestor. This is consistent with population dynamics of frequent colonizations by single sib-mated females of common origin, and extinctions of populations after few generations. Although drift or single mutations can lead to population divergence at a relatively short time scale, it is possible that dynamic population processes homogenize these effects at longer time scales.
authors.affiliation: Mitrani Department of Desert Ecology, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boker Campus, 84990, Israel; Genetics, Ecology and Evolution, Department of Bioscience, Aarhus University, Ny Munkegade, 116, 8000, Aarhus C, Denmark. tut.berger.tal@gmail.com.
authors.forename: Reut
authors.initials: R
authors.lastname: Berger-Tal
authors.forename: Cristina
authors.initials: C
authors.lastname: Tuni
authors.forename: Yael
authors.initials: Y
authors.lastname: Lubin
authors.forename: Deborah
authors.initials: D
authors.lastname: Smith
authors.forename: Trine
authors.initials: T
authors.lastname: Bilde
mesh_terms: D000818:Animals; D005260:Female; D056084:Genetic Fitness; D014644:Genetic Variation; D006720:Homozygote; D006824:Hybridization, Genetic; D007178:Inbreeding; D008297:Male; D011153:Population / Q000235:genetics; D012098:Reproduction / Q000235:genetics; D013112:Spiders / Q000235:genetics* / Q000502:physiology
keywords: Inbreeding depression; inbred sociality; local adaptation; population incompatibility; purging; social spiders